1. Field of the Invention
The invention relates to a multiple disk clutch and to a method and an apparatus for forming the clutch drum of the multiple disc clutch.
2. Description of the Related Art
Multiple disc clutches are integrated into gear trains of automatic transmissions and selectively transmit power between rotational components. A typical multiple disc clutch includes a clutch drum housing a hydraulic servo therein, a clutch hub arranged radially inward of the clutch drum, and clutch plates arranged between the clutch drum and the clutch hub. The multiple disc clutch is engaged when the piston of the hydraulic servo is pushed against the clutch plates by application of a hydraulic pressure. In this manner the drive plates, usually separator plates, are pressed against driven plates, usually frictional discs. When the clutch is engaged, a small axial vibration (hereinafter "shudder") is produced in the piston of the hydraulic servo because of pulsation of the applied hydraulic pressure. Therefore, when the piston pushes directly against the plates, the vibration is transmitted to the plates. Especially, when torque transmission is started by engagement of the clutch, a shudder occurs due to change of the engagement pressure. For reducing the shudder produced by the pulsation of the hydraulic pressure, a cushion plate is arranged between the piston and the clutch plates.
The separator plates of the multiple disc clutch are annular discs and, as shown in FIG. 9, have a plural number of splines 21' projecting outward. The separator plates are movable axially relative to the clutch drum but are held against rotation relative to the clutch drum by splined engagement between the splines 21' and the spline grooves 11' formed on the inner surface of the clutch drum. The cushion plate is formed as an annular disc spring and has a plural number of splines 31' formed projecting outward, like those of the separator plates. The cushion plate is movable axially relative to the clutch drum but is held against rotation relative to the clutch drum by splined engagement between the splines 31' and spline grooves 11'. The cushion plate cushions and transmits the applied pressure from the servo piston to the separator plates. The cushion plate has a predetermined camber between its outer periphery and its inner periphery. Due to the configuration of the cushion plate, the load is transmitted by contact between the inner periphery of the cushion plate and the piston and between the outer periphery of the cushion plate and the separator plates. A predetermined spring characteristic is thereby provided by the cushion plate.
In the conventional multiple disk clutch, the predetermined spring characteristic of the cushion plate is set without consideration for contact at the splines. But, because the spline projections 31' of the cushion plate and the spline projections 21' of the clutch plates are in contact within the common spline grooves 11', the load on the clutch plates is reduced. Further, a predetermined spring characteristic of the cushion plate cannot be maintained during the piston stroke because the cushion plate is an annular disk spring having a predetermined camber and the spring force differs radially across the area of the cushion plate contacting the clutch plate.
To prevent the splines 31' of the cushion plate from contacting the clutch plates, it has been proposed to form tapers on the splines 31' of the cushion plate. However, this approach adds to the cost of manufacture.